if their business is usually on the N shore or the city they are not going to venture out further but if you prebook an appt it may be enough for them to relocate for a day or two.
There are plenty of women who work in that area, you just have to ask.

I don't see a lot of posts for Newton or Needham, but a reasonable amount for Waltham (bordering Newton) and Dedham (bordering Needham).  The famous agency RSG is in those areas and in fact a good number of providers that appear as if they must be in Boston work in those areas as well.  I personally would encourage providers to consider Waltham (or perhaps Burlington although less convenient for me) as an alternative to downtown.  From the hobbyist perspective we get free parking and often less of a traffic concern.